This invention relates to an improved process for the preparation of nitrosobenzene by the catalytic reduction of nitrobenzene.
According to the classical process, nitrosobenzene is obtained through the oxidation of phenyl hydroxylamine by means of a chromic acid mixture (Bamberger, B. 27, 1955), or by means of a neutral potassium permanganate solution (Bamberger et al., B. 31, 1524; B. 32, 342; A. 311, 78), through the oxidation of aniline by means of monoperoxysulfuric acid (Caro, Z. angew. Chem. 11, 845; German Pat. No. 110,575), or through reduction of nitrobenzene by means of zinc powder (W. J. Mijs et al., Recueil 77, 746-752). A series of other methods for the making of nitrosobenzene are also known, but they are not suitable for either small-scale or large-scale preparation of nitrosobenzene (Beilsteins Handbuch der Organischen Chemie, vol. 5, H. 230, I 123, II 169 and III 585).
In the small-scale preparation of nitrosobenzene one may commence by catalytically reducing nitrobenzene, using carbon monoxide, suitable aldehydes, ketones, or alcohols. According to a method described in German Pat. No. 1,810,828, nitrobenzene may be reduced with carbon monoxide at temperatures from 100 to 140.degree. C., wherein the catalyst consists of two or more of the heavy metals Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ge, Zr, Mo, Ag, Sn, Sb, La, Ce, Nd, Ta, W, Re, Au, Hg, Tl, Pb, Bi and Th, in the form of their oxides, hydroxides, carbonates, or basic phosphates, or in the form of partial reduction products. The catalyst may be prepared by means of a process consisting in essence of a joint precipitation from a solution, or a joint heating of the mentioned heavy metals in the form of their hydroxides, or in the form of thermally unstable salts, or mixtures thereof. According to a process described in British Pat. No. 1,322,531, with higher yield and selectivity, the catalyst to be used in the reduction of nitrobenzene by means of carbon monoxide is prepared in such a way that, first, a layer of one of the oxides of silver, cooper or lead is applied by thermal decomposition of a suitable metal salt on a carrier material, such as pumice, asbestos, diatomaceous earth, etc. and subsequently, above the first oxide layer, there is applied a second layer of one of the oxides of manganese, iron, copper, chromium, vanadium or cerium. Only certain combinations of the two layers are possible.
Another catalyst suitable for the reduction of nitrobenzene to nitrosobenzene by means of carbon monoxide is described in British Pat. No. 1,259,504. It is obtained by treating a manganese oxide precipitate still containing bound alkali with a solution of one or several of the metals Ti, V, Cr, Fe, Co, Ni, Cu, Zr, Mo, Ag, Sn, Sb, Ta, W, Re, Au, Hg, Tl, Pb and Bi, as a result of which the alkali is replaced by the heavy metal, followed by filtering off and drying of the solid substance.
The catalyst described in Dutch published patent application No. 7,005,588, which is prepared from a magnesium oxide precipitate containing alkali and treated with the solution of salts of the metals Co, Cu, Ag and Pb, is said to be suitable for the same purpose. Furthermore, catalysts are recommended for the reduction of nitrobenzene to nitrosobenzene by means of carbon monoxide, which consist of heavy metal formates (British Pat. No. 1,251,836), heavy metal oxalates (British Pat. No. 1,251,844), or of palladium/carbon (Japanese Pat. No. 4,731,937). According to the process of Japanese Pat. No. 9,126,633, nitrosobenzene can also be prepared through photoreduction by means of certain metal carbonyl compounds.
The catalytic reduction of nitrobenzene to nitrosobenzene by means of aldehydes, ketones, or alcohols is known from German Pat. No. 2,346,388. As reducing agents, mention may be made of acetaldehyde, metaldehyde, acetone, methylethylketone, butanol-2, allyl alcohol, 2-methylpropanol, n-butanol, n-propanol, isopropanol, ethanol and methanol. The catalysts to be used consist of one of the heavy metals Sb, Bi, Ce, Cr, Co, Cu, Ge, Au, Fe, La, Pb, Mn, Hg, Mo, Nd, Ni, Re, Ag, Ta, Tl, Th, Sn, Ti, W, V and Zr in association with oxygen atoms or hydroxyl, carbonate or phosphate ions, and additionally contain at least one of the other mentioned heavy metals, which forms contaminating atoms in the lattice.